1. Field of the Invention
The present invention relates to a recording medium suitable for use in recording using water-based inks, ink-jet recording method and a dispersion. In Particular, this invention relates to a recording medium which can provide images high in optical density, bright in color tone and high in resolution, and has excellent ink-absorbing capacity, an ink-jet recording method using such a recording medium, and a dispersion of an alumina hydrate, which is suitable for use in production of the recording medium.
2. Related Background Art
In recent years, an ink-jet recording system, in which minute droplets of an ink are flown by any of various working principles to apply them to a recording medium such as paper, thereby conducting recording of images, characters and/or the like, has been quickly spread as a recording apparatus for various images in various applications including information instruments because it has features that recording can be conducted at high speed and with a low noise, color images can be formed with ease, recording patterns are very flexible, and development and fixing process are unnecessary. Further, it begins to be applied to a field of recording of full-color images because images formed by an multi-color ink-jet recording system are comparable in quality with multi-color prints by a plate making system and photoprints by a color photographic system, and such records can be obtained at lower cost than the usual multi-color prints and photoprints when the number of copies is small. With the improvement in recordability, such as speeding up and high definition of recording, and multi-coloring of images, recording apparatus and recording methods have been improved, and recording media have also been required to have higher properties.
In order to satisfy such requirements, a wide variety of recording media have been proposed. For example, Japanese Patent Application Laid-Open No. 52-53012 discloses paper for ink-jet, in which a base paper web low in sizing degree is impregnated with a surface coating. Japanese Patent Application Laid-Open No. 53-49113 discloses paper for ink-jet, in which a sheet containing urea-formalin resin powder therein is impregnated with a water-soluble polymer. Japanese Patent Application Laid-Open No. 55-5830 discloses paper for ink-jet recording, in which a coating layer having good ink absorptiveness is provided on a surface of a base. Japanese Patent Application Laid-Open No. 55-51583 discloses that amorphous silica is used as a pigment in a coating layer. Japanese Patent Application Laid-Open No. 55-146786 discloses that a coating layer formed of a water-soluble polymer is used.
In U.S. Pat. Nos. 4,879,166 and 5,104,730, and Japanese Patent Application Laid-Open Nos. 2-276670, 4-37576 and 5-32037, there have been proposed recording sheets having a layer using an alumina hydrate of a pseudoboehmite structure.
As described in U.S. Pat. Nos. 4,374,804 and 5,104,730, and Japanese Patent Application Laid-Open Nos. 58-110287 and 4-37576, it has also been conducted to form an ink-receiving layer of a multi-layer structure using a silica or alumina material.
However, the conventional recording media have involved the following problems:
1) U.S. Pat. No. 5,104,730, and Japanese Patent Application Laid-Open Nos. 2-276670, 2-276671 and 3-275378 disclose recording media having extremely narrow distribution of pore radius. As disclosed in Japanese Patent Application Laid-Open Nos. 4-267180 and 5-16517, however, individual dyes for inks (cyan, magenta, yellow and black) and solvents for the inks are selectively adsorbed in pores of a specific size. Therefore, bleeding may occur on prints if the composition of ink is changed.
The bleeding refers to a phenomenon that edges of boundaries of multi-color printed areas can not be resolved because of feathering caused when ink is still fluid before it is fixed in the ink-receiving layer.
2) U.S. Pat. No. 5,104,730, and Japanese Patent Application Laid-Open Nos. 2-276670, 2-276671 and 3-275378 disclose recording media having pore radius distribution as narrow as 10 to 30 .ANG. in average pore radius. In this pore radius distribution, dye adsorptiveness is good, while the absorptiveness of solvent is insufficient, resulting in the occurrence of beading.
The beading mentioned in the present invention refers to a phenomenon in which dots irregularly move in the plane direction of the surface of an ink-receiving layer when ink is still fluid before it is fixed in the ink-receiving layer, thus forming new aggregates together with adjacent dots to cause an unevenness in the density of recorded images.
3) In printing of color images, inks increase in quantity. The inks printed cannot be completely absorbed in pores, but run out on the surface of an ink-receiving layer, so that bleeding occurs, resulting in deterioration in print quality.
4) High-speed printing requires to have good drying ability. However, absorbing rate is insufficient, and the printed surface is hence not dry when discharged out of a printing apparatus, so that output images may be possibly impaired by contact.
5) There is a problem that the solids concentration of a dispersion of a pigment or the like cannot be increased because the viscosity of the dispersion increases with time, resulting in a failure to apply it. As a measure for the solution of the problem, Japanese Patent Application Laid-Open No. 4-67986 discloses a process in which the polymerization degree of a polymer as a binder is lowered. However, this process involves problems of defective appearance such as cracking in an ink-receiving layer, reduction in water fastness, and the like, and hence still requires a further improvement.
6) There is a problem that since the viscosity of the dispersion is high, its solids concentration cannot be increased. As a measure for the solution of the problem, Japanese Patent Application Laid-Open No. 4-67985 discloses a process in which an acid such as a monocarboxylic acid is added as a dispersant. However, this process is accompanied by productive problems that offensive odor is given, and corrosion is caused.
7) In order to improve ink absorptiveness and resolution of images, U.S. Pat. Nos. 4,780,356, 4,374,804 and 5,104,730, Japanese Patent Publication No. 3-72460, and Japanese Patent Application Laid-Open Nos. 55-11829, 58-110287, 62-270378 and 4-37576 disclose a process in which an ink-receiving layer of a two or more multi-layer structure is formed. However, the process involves a problem that coating and drying must be conducted at least twice for forming the ink-receiving layer, and so the number of processes increases. In addition, since the physical property values of the individual layers are different from each other, there are also problems of changes with time, defective appearance such as cracking in the ink-receiving layer, and separation and peeling of the layers from each other upon printing or the like.
8) Japanese Patent Application Laid-Open No. 3-281384 discloses an alumina hydrate forming an aggregate like a needle, which is in the form of a column having an aspect ratio of not higher than 3 and unidirectionally oriented, and a process for forming an ink-receiving layer using the alumina hydrate. However, since particles of the alumina hydrate are oriented and compacted, spaces among the alumina hydrate particles in the ink-receiving layer tends to narrow. Therefore, the pore radius is partial to a narrow side, and distribution of pore radius has a tendency to narrow. As a result, there is a problem that beading occurs as described above.